It is known that 1,4-butanediol (hereinafter sometimes abbreviated as “1,4BG”) is an extremely useful substance which is used as a raw material of various solvents or derivatives. A variety of methods for industrially producing 1,4BG have hitherto been developed. For example, there are exemplified a method in which butadiene is used as a raw material, an acetoxylation reaction is conducted by using the raw material butadiene, acetic acid, and oxygen to obtain diacetoxybutene that is an intermediate, and the diacetoxybutene is hydrogenated and hydrolyzed to obtain 1,4BG (Patent Document 1); a method in which maleic acid, succinic acid, maleic anhydride, and/or fumaric acid is used as a raw material, and such a raw material is hydrogenated to obtain a crude hydrogenation product containing 1,4BG (Patent Document 2); a method in which butynediol obtained by bringing acetylene as a raw material into contact with a formaldehyde aqueous solution is hydrogenated to produce 1,4BG (Patent Document 3); and the like.
Though tetrahydrofuran (hereinafter sometimes abbreviated as “THF”) that is a derivative obtained from 1,4BG as a raw material is in general used as a solvent, it is also used as a raw material of polyether polyols (specifically polytetramethylene ether glycol). As for a method for producing THF from 1,4BG, Patent Document 4 describes that in a method for continuously producing THF by allowing a reaction mixture containing 1,4BG to react over a heteropolyacid catalyst, by allowing the reaction mixture to contain 2-(4-hydroxybutoxy)-tetrahydrofuran and less than 1 ppm of a basic nitrogen component, the life of the heteropolyacid catalyst can be made long. In addition, polybutylene terephthalate (hereinafter sometimes abbreviated as “PBT”) is other derivative obtained from 1,4BG as a raw material. Patent Document 5 describes a method for producing PBT in which in the esterification reaction, in order to avoid loss of 1,4BG as a raw material due to side reaction to produce THF, a reaction condition (e.g., a concentration of catalyst raw material, a reaction pressure, a ratio of terephthalic acid and 1,4BG, etc.) is controlled.